ASSESSING GROSS EFFICIENCY AND PROPELLING EFFICIENCY IN SWIMMING

Determining the efficiency (and the economy) of a movement is a primary goal for those interested in understanding, and possibly improving, human locomotion and/or sport’s performance. This goal is particularly difficult to achieve in swimming where different “efficiencies” could be computed based on the partitioning of mechanical power output into its useful and non useful components as well as because of the difficulties in measuring the forces a swimmer can exert in water. In this paper the “possible range” of overall (gross) and propelling efficiency values for swimming humans is estimated and discussed

FORCE GENERATION IN SPRINT RUNNING IS RELATED TO MUSCLE PROPERTIES IN MALE SPRINTERS

The aim of this study was to investigate the relationship between muscle properties (MP) and force production (F) during a sprint running acceleration phase in 18 male sprinters (Age: 24.4±4 years; personal best: 10.66±0.5 s). MP (muscle thickness, fascicle length and pennation angle) of the lower limb muscles were measured by B-mode ultrasonography and F was modelled at each instant by derivation of running velocity. All MP variables showed significant correlations with peak force values (p\u3e0.01): longer fascicle length, greater thickness and lower pennation angle are associated with greater force production and subsequent acceleration ability

BALANCE OF BIOMECHANICAL AND PHYSIOLOGICAL CONTRIBUTIONS TO SWIMMING PERFORMANCE

Swimming is a unique activity carried out in a unique environment. Performance depends on interplay between biomechanical and bioenergetic aspects, thus if we can understand their interaction, as a function of velocity, we can understand the biophysics of swimming. The relationship between stroke frequency and velocity and their impact on drag and efficiency are critical. The biomechanical aspects dictate the velocity-dependent metabolic demands of swimming, thus the maximal performance is determined by the balance of metabolic power among aerobic and anaerobic pathways. Training is a determinant of swimming performance, and applying bioenergetic principles could improve performance

Low-cost electromyography: validity against a commercial system depends on exercise type and intensity

The aim of this study was to assess the validity of a custom-made low cost (LC) and a commercial surface EMG apparatus in controlled experimental conditions and different exercise types: maximal voluntary contractions (MVC) at 105, 90, 75, 60, 45 and 30\ub0 knee angle and explosive fix-end contractions of the knee extensors (75\ub0) at an isometric dynamometer. sEMG of vastus lateralis was recorded from the same electrodes simultaneously, then analyzed in the same way; sEMG were finally expressed in percentage of those collected at 75\ub0MVC. LC underestimated the sEMG signal at the more extended knee angles (30-60\ub0), significant difference was observed only at 30\ub0. In the explosive contractions no differences between devices were observed in average and peak sEMG, as well as in the time to peak and the activation time. Bland-Altman tests and correlation parameters indicate the LC device is not sensible enough to detect the time to peak and the peak values of the sEMG signal properly. Results suggest low-cost systems might be a valid alternative to commercial ones, but attention must be paid when analyzing rapid events

Muscle belly gearing positively affects the force-velocity and power-velocity relationships during explosive dynamic contractions

Changes in muscle shape could play an important role during contraction allowing to circumvent some limits imposed by the fascicle force-velocity (F-V) and power-velocity (P-V) relationships. Indeed, during low-force high-velocity contractions, muscle belly shortening velocity could exceed muscle fascicles shortening velocity, allowing the muscles to operate at higher F-V and P-V potentials (i.e., at a higher fraction of maximal force/power in accordance to the F-V and P-V relationships). By using an ultrafast ultrasound, we investigated the role of muscle shape changes (vastus lateralis) in determining belly gearing (muscle belly velocity/fascicle velocity) and the explosive torque during explosive dynamic contractions (EDC) at angular accelerations ranging from 1000 to 4000°.s-2. By means of ultrasound and dynamometric data, the F-V and P-V relationships both for fascicles and for the muscle belly were assessed. During EDC, fascicle velocity, belly velocity, belly gearing, and knee extensors torque data were analysed from 0 to 150 ms after torque onset; the fascicles and belly F-V and P-V potentials were thus calculated for each EDC. Absolute torque decreased as a function of angular acceleration (from 80 to 71 Nm, for EDC at 1000 and 4000°.s-1, respectively), whereas fascicle velocity and belly velocity increased with angular acceleration (P < 0.001). Belly gearing increased from 1.11 to 1.23 (or EDC at 1000 and 4000°.s-1, respectively) and was positively corelated with the changes in muscle thickness and pennation angle (the changes in latter two equally contributing to belly gearing changes). For the same amount of muscle's mechanical output (force or power), the fascicles operated at higher F-V and P-V potential than the muscle belly (e.g., P-V potential from 0.70 to 0.56 for fascicles and from 0.65 to 0.41 for the muscle belly, respectively). The present results experimentally demonstrate that belly gearing could play an important role during explosive contractions, accommodating the largest part of changes in contraction velocity and allowing the fascicle to operate at higher F-V and P-V potentials

The relationship between power generated by thrust and power to overcome drag in elite short distance swimmers

At constant average speed (v), a balance between thrust force (Ft) and drag force (Fd) should occur: Ft-Fd = 0; hence the power generated by thrust forces (Pt = Ft\ub7v) should be equal to the power needed to overcome drag forces at that speed (Pd = Fd\ub7v); the aim of this study was to measure Pt (tethered swims), to estimate Pd in active conditions (at sprint speed) and to compare these values. 10 front crawl male elite swimmers (expertise: 93.1 \ub1 2.4% of 50 m world record) participated to the study; their sprint speed was measured during a 30 m maximal trial. Ft was assessed during a 15 s tethered effort; passive towing measurement were performed to determine speed specific drag in passive conditions (kP = passive drag force/v2); drag force in active conditions (Fd = kA\ub7v2) was calculated assuming that kA = 1.5\ub7kP. Average sprint speed was 2.20 \ub1 0.07 m\ub7s-1; kA, at this speed, was 37.2 \ub1 2.7 N\ub7s2\ub7m-2. No significant differences (paired t-test: p > 0.8) were observed between Pt (399 \ub1 56 W) and Pd (400 \ub1 57 W) and a strong correlation (R = 0.95, p < 0.001) was observed between these two parameters. The Bland-Altman plot indicated a good agreement and a small, acceptable, error (bias: -0.89 W, limits of agreement: -25.5 and 23.7 W). Power thrust experiments can thus be suggested as a valid tool for estimating a swimmer's power propulsion

Influence of muscle-belly and tendon gearing on the energy cost of human walking

This study combines metabolic and kinematic measurements at the whole-body level, with EMG and ultrasound measurements to investigate the influence of muscle-tendon mechanical behavior on the energy cost (Cnet) of walking (from 2 to 8 km·h−1). Belly gearing (Gb = Δmuscle-belly length/Δfascicles length) and tendon gearing (Gt = ∆muscle-tendon unit length/∆muscle-belly length) of vastus lateralis (VL) and gastrocnemius medialis (GM) were calculated based on ultrasound data. Pendular energy recovery (%R) was calculated based on kinematic data, whereas the cumulative activity per distance travelled (CMAPD) was calculated for the VL, GM, tibialis anterior, and biceps femoris as the ratio between their EMG activity and walking speed. Finally, total CAMPD (CMAPDTOT) was calculated as the sum of the CMAPD of all the investigate muscles. Cnet and CMAPDTOT showed a U-shaped behavior with a minimum at 4.2 and 4.1 km·h−1, respectively; while %R, VL, and GM belly gearing showed an opposite trend, reaching a maximum (60% ± 5%, 1.1 ± 0.1 and 1.5 ± 0.1, respectively), between 4.7 and 5 km·h−1. Gt was unaffected by speed in GM (3.5 ± 0.1) and decreased as a function of it in VL. A multiple stepwise linear regression indicated that %R has the greatest influence on Cnet, followed by CMAPDTOT and GM belly gearing. The role of Gb on Cnet could be attributed to its role in determining muscle work: when Gb increases, fascicles shortening decreases compared with that of the muscle-belly, thereby reducing the energy cost of contraction

Mechanical power, thrust power

The purpose of this study was to explore the relationships between mechanical power, thrust power, propelling efficiency and sprint performance in elite swimmers. Mechanical power was measured in 12 elite sprint male swimmers: i) in the laboratory, by using a whole body swimming ergometer (W’TOT); and ii) in the pool, by measuring full tethered swimming force (FT) and maximal swimming velocity (Vmax): W’T = FT .Vmax. Propelling efficiency ( P) was estimated based on the “paddle wheel model“ at Vmax. Vmax was 2.17 ± 0.06 m . s-1, P was 0.39 ± 0.02, W’T was 374 ± 62 W and W’TOT was 941 ± 92 W. Vmax was better related to W’T (useful power output: R=0.943, P<0.001) than to W’TOT (total power output: R=0.744, P<0.01) and this confirms the use of the full tethered test as a valid test to assess power propulsion in sprinters and to estimate swimming performance. The ratio W’T/ W’TOT (0.40 ± 0.04) represents the fraction of total mechanical power that can be utilized in water (e.g. P) and was indeed the same as that estimated based on the “paddle wheel model”; this supports the use of this model to estimate P in swimming

Water-based training enhances both physical capacities and body composition in healthy young adult women

PURPOSE: The purpose of this study was to determine the effectiveness of a 9 weeks aquatic training program on aerobic capacity, muscle strength, flexibility, balance and body composition in 34 healthy young adult women. METHODS: Five typical water based exercises (WE) of known intensity were utilized during the classes; intensity ranged from “moderate” to “hard” according to ACSM criteria (RPE range 12–14). RESULTS: The group physical activity level and food intake were not significantly different before and after training. A significant decrease for the skin folds sum (−4.6 %) and for %fat mass (−3.8 %) calculated according to skin folds technique was found after training. DXA regional data showed a significant increase in the fat-free mass of arms (2.4 %) and trunk (0.9 %). According to the Astrand step test, the training program led to an increase of estimated maximal oxygen uptake (14.9 %) and a decrease in sub-maximal Heart Rate (−6.9 %). A significant change in the majority of the physical capacities tested was found: abdominal and upper body muscular endurance (21 and 36 %, respectively), leg flexors and extensors maximal strength (12 and 8 %, respectively) as well as balance (34 %) all improved after training (p < 0.05). CONCLUSIONS: A training program based on WE of known intensity and tailored to the ACSM recommendations can significantly improve cardio respiratory fitness, muscular endurance, strength, balance and some aspects of body composition in active young adult women

Different methods for monitoring intensity during water-based aerobic exercises.

The aim of this study was to compare different measurement techniques (indirect calorimetry, IC; heart rate monitoring, HR; an activity monitoring system, AH; rates of perceived exertion, RPE) to estimate physical activity intensity (light, moderate, vigorous) during water-based aerobic exercises (WE). Twelve healthy young women performed five common WE of 10-min duration at three frequencies in an indoor swimming pool. Data recorded from the 5th to 9th minute of exercise were averaged to obtain mean [Formula: see text] (IC), HR and AH values; RPE was recorded at the end of each WE. Oxygen uptake was also estimated from HR data using three different [Formula: see text] versus HR regression equation models. Significant correlations (p\ua0\ua00.7 in all cases). An ANOVA test showed no significant differences between all predicted and measured [Formula: see text] values; however, when the Bland & Altman analysis was considered, AH data showed the larger explained variances (95\% CI) and the larger standard errors. These data indicate that the most accurate way to estimate physical activity intensity during WE is based on HR measurements